The present invention relates to mine roof expansion anchors of the type having a radially expansible shell and a tapered plug moveable axially within the shell to effect expansion thereof. More specifically, the invention relates to novel structures of mine roof expansion anchors and tapered plug elements thereof for installation together with a resin grouting mix in a drill hole in a mine roof, or the like, and to methods of installation of combined resin-mechanical anchors.
For many years, one of the most popular means of providing support and reinforcement to mine roofs and other subterranian structures has been the mechanical expansion anchor. Such anchors have been proposed in a wide variety of designs having in common a radially expansible shell portion and a tapered plug having an internally threaded, axial bore. The threaded end of a bolt or other elongated rod is engaged with the bore of the tapered plug and the shell is suitably supported in surrounding relation to the smaller end of the plug. The end of the rod carrying the anchor is inserted into a pre-drilled hole in the rock structure, and the shell is expanded into tight engagement with the drill hole wall by rotation of the bolt to move the larger portion of the plug into the shell.
More recently, the effectiveness and useful life of anchorages have been enhanced by the use of quick-setting resin grouting mixes conjointly with mechanical anchors. Such mixes are commercially available in elongated, breakable tubes or cartridges having a diameter approximating that of the drill hole, and separate compartments containing a resin and a catalyst which are in a flowable condition prior to mixing. The lengths of the resin cartridge and bolt are so related to the depth of the drill hole that forced insertion of the bolt crushes the cartridge against the end of the drill hole, releasing the two components which are mixed to the extent necessary as they pass through and around the anchor and end of the bolt, and by rotation of the bolt to move the plug axially into the shell. Upon mixing of the components, the grouting mix hardens in a few seconds.
Since the large end of the tapered plug is positioned nearest the resin cartridge and is often substantially as large in diameter as the drill hole, provision must be made for allowing the grouting mix components to flow past the plug and through the shell to surround the end of the bolt. Among a significant number of U.S. patents noting the need for resin flow passages in such installations are U.S. Pat. Nos. 4,859,118, 4,969,778 and 5,009,549. In the anchors of these and other patents, the passages are provided by axial grooves between external compression surfaces on the tapered plug. That is, the plurality of radially expansible leaves, typically two, three or four in number, which form the shell structure are circumferentially spaced from one another and have internal surfaces which are contacted by opposing surfaces of the tapered plug. As the larger end of the plug is moved axially between the leaves to force outward expansion thereof, the leaves are compressed between the plug and the drill hole wall and an inwardly compressive force is exerted on the surface portions of the plug which contact the shell leaves. Prior art expansion anchors for use with resin cartridges have traditionally provided resin flow passages in the portions of the plug between the compression surfaces, i.e., between the surfaces which directly oppose the internal surfaces of the shell leaves.
It is a principal object of the present invention to provide a mechanical expansion anchor for use in conjunction with a resin cartridge to anchor a mine roof bolt in a drill hole wherein the anchor has an improved design to enhance the flow of resin mix components through and around the anchor.
Another object is to provide an improved tapered camming plug for a mine roof anchor which enhances performance of the anchor when used with a resin grouting mix.
A further object is to provide a tapered plug with uniquely positioned resin flow passages for use in combined resin-mechanical anchorages for rock structure supports.
Still another object is to provide a novel method of anchoring the distal end of a mine roof bolt in a drill hole using both a mechanical anchor and resin to achieve enhanced performance.
Other objects will in part be obvious and will in part appear hereinafter.